Signaling system



March 21, 1944. c, E. BEACH 2,344,500

SIGNALING SYSTEM Filed Feb. 19, 1940 4 Sheets-Sheet 1 N95 TEE 6T8 T/ON Buzz Mm 21, 1944. Q E, B A 2,344,500

SIGNALING SYSTEM Filed Feb. 19, 1940 4 Sheets-Sheet 3 //v VEN TOR March 21, 1944. Q BEACH 2,344,500

SIGNALING SYSTEM Filed Feb. 19, 1940 4 Sheets-Sheet 4 FIG-ll INVENTOR Patented Mar. 21, 1944 23sec UNITED STATES PATENT OFFICE SKGNALING SYSTEM Clarence E. Beach, Bingharnton, N. Y. Application February 19, 1949, Serial No. 319,628

25 Claims.

I This invention relates to signaling systems, and

more particularly to signaling systems of the type often designated as auxiliary systems and having auxiliary or sub-stations for causing signaling activity of associated main signal initiating stations. This invention is especially suited, although by no means limited, to use in connection with circuits including code signal formulating main stations, in which circuits current flow is normally maintained, and between which circuits and the ground, or other common return conductor, an electromotive force is normally maintained whereby response to signal formulation may be effected notwithstanding various abnormal circuit conditionings.

Signaling systems have heretofore been devisedin which each main station comprises a starting or tripping magnet for energization by current flow from the main fire alarm signaling circuit intended for response thereto, which magnet is normally short-circuited by a loop serially including sub-stations operable to interrupt current flow in the loop for the purpose of setting the main station into action. Such systems are frequently designated as shunt type auxiliary systems, and main'stations of such systems are frequently referred to as auxiliarized fire alarm boxes. Disclosure of shunt type systems may be found in applicants Patent No. 1,093,679, dated April 21, 1914.

Conventional forms of fire alarm systems utilizing code formulating stations, of types generally such as that disclosed by the patent just referred to, provide circuits often serially including a score or more of such boxes, and it has been found to be desirable to incorporate into such systems facilities whereby loss of code signals may be minimized or completely avoided, notwithstanding the development of circuit defects such as breaks and grounds, as well as crosses whereby one. or more boxes are short circuited.

Applicants Patent No. 1,999,859, dated April 30', 1935, not only discloses fire alarm box signaling mechanism which, when set in action, will formulate the intended code signal by alternately breaking and closing its associated circuit, subject to so-called, non-interference and succession control as well understoodby thoseskilled in this art, but that patent further discloses means for effecting formulation of the code signal in a path between one, the other or both sides of the series circuit and the ground or other socalled common return or independent conductor, following determination by such mechaing occasions when there is no current flow in the portion of the main signaling circuit in which such master box is connected, either because such box is short-circuited or because current flow is interrupted by an accidental break in the circuit at one side or the other of such box.

It is, therefore, one of the principal objects of this invention to provide an auxiliary signaling system in which operation of a sub-station will result in its associated master station being set into operation notwithstanding any abnormal conditioning of the main circuit such as would be insufficient to cause loss of the code signal of such main station once it were set in operation.

It is a further object to provide, in such a signaling system, means whereby signal formulation in the associated main circuit, irrespective of whether occurring under normal or emergency conditions, will not be interrupted or impaired resultant from actuation of any sub-station or stations.

It is a further object to provide, in such signaling systems, construction and arrangement of parts such that assurance of responsive operation of an associated main station will not be impaired in the event that a plurality of substations is actuated at or about the same time.

In the use of prior forms of shunt ty-pe auxiliary systems, there have been instances in which an objectionable number of needless signals have resulted from accidental auxiliary loop breakage.

It is, therefore, a further object of this invention to provide a shunt type system which is susceptible of embodiment in a form and arrangement whereby tripping of auxiliarized or main stations will not result from accidental shunt loop breakage.

The transmission of an objectionable number of needless signals has also been experienced in the use of some shunt type auxiliary systems, particularly where the main line circuit has been subjected to current surges, as from lightning or from accidental contacts with foreign circuits. It is evident that, in 'such systems, as

heretofore constructed, some part of the main line current flow always passes through the winding of the tripping magnet, although the major portion may be divided out, pursuant to Ohms Law, and pass through the closed shunt loop. Assuming, however, that the usual main line current flow is on the order of 0.1 ampere, and that the trip magnet is made dependably operable at 0.06 ampere, in order to provide a factor of safety (as is common practice), and that the relative resistances of the magnet winding and of the shunt loop current paths is such that but onefifth, or even one-tenth, of the main line current fiow reaches the winding of the tripping magnet while the shunt loop is intact (which would be 0.02 or 0.01 ampere at normal main current flow) should a surge momentarily increase the main line current fiow to 0.03 or 0.06 ampere or more, in the respective circumstances, effective energization of the tripping magnet would result.

It is, therefore, another important object of this invention to provide a shunt type auxiliary system which may be embodied in a form such that tripping of master or auxiliarized main line stations will not result from current surges in the main line circuit.

Inasmuch as attainment of the object just stated, in accordance with this invention, in-

volves the utilization of a master station tripping magnet having a self-neutralizing winding, it is a subsidiary object of this invention to devise a method of applying such a winding whereby minimum opportunity will be afforded for development of what may be termed anomalous poles such as are likely to become significant when opposing sectional windings extend along substantial portions of the length of an electromagnet core and are subjected to comparatively large current flow, with resultant development of a free pole or poles of such strength as to cause response of associated armature.

In order that desired results may be obtained when this invention is utilized in connection with signaling systems in which no signaling electromotive force is normally (or, in some instances, at any time) maintained between the main signaling circuit and the earth or any other common return conductor; and/or where, for any reason, it is deemed objectionable to provide electrical connection between the main signaling circuit and conductors connecting sub-stations either at particular times or at all times: It is a still further purpose of this invention to provide a system in which all desired results may be obtained through use of sub-stations (with or without answer back equipment) connected with the master station through conductors which may at all times be isolated from the main circuit, or which may be associated at times with the main circuit, for obtaining desired electrical test and supervision therefrom, and may at other times be completely isolated from the main circuit in a very simple manner, all without impairing the functional features of the system other than in respect to the loss of such main circuit test and supervision, and (as by providing magneto generators at sub-stations) without thereby incurring the use of primary or secondary batteries or other forms of current supply mechanism needing periodic replenishment or supervision or subject to extraneous suspension or disconnection.

In meeting practical operating conditions, many instances are found in which it may be deemed advantageous to minimize the number of required conductors, or otherwise to simplify or to delete certain features of this invention, notwithstanding resultant loss of one or more functional results deemed highly important under other circumstances.

It is, therefore, a still further object of this invention to provide a system which is suited for various modifications and simplifications, involving deletion of various structural features and functions, whereby to meet differing local conditions and requirements.

Other objects, together with their inherent advantages, will be in part obvious and in part specifically pointed out in connection with the ensuing description of the illustrated embodiments of this invention.

In applying this invention to signaling systems employing normally closed main line circuits having a constantly available emergency signaling path between such circuits and the ground or some other common return conductor: Main stations are provided having tripping magnets which are subject to energization by normal main line current flow; loops are associated with such magnets for maintaining them in normally deenergized conditioning; sub-stations are connected by these loops, each having mechanism which may be manually or otherwise actuated or set in action for effecting a series of two or more changes in loop conditioning for the purpose of causing energization of an associated main station trip magnet. 7

Such sub-station mechanism is of a character suchthat its first step of operation serves to alter the conditioning of associated loop or loops in such manner that the associated trip magnet will be immediately energized if normal main line current fiow is then available therefor, and such that, if the normal main line current path is then interrupted because a code signal is in course of formulation therein, such magnet will be energized during the next ensuing closure incident to the formulation of such code signal.

Ensuing action or actuation of such sub-sta tion mechanism establishes a connection or connections, between associated loop or loops and the ground or other common return conductor, whereby trip magnet energization will be effected in the event that the main line circuit is broken at one side or the other of the main station, and/or in the event that the main station is short-circuited.

Tripping mechanism associated with and for response to energization of each trip magnet, sets in action associated main line signal formulating mechanism.

Said tripping mechanism, in acting, also completely disconnects sub-station loop conductors from the main line circuit, besides excluding the resistance of the tripping magnet winding from the main line circuit.

In accordance with one aspect of this invention, the sub-station mechanism may be made responsive to a plurality of actuating steps separated by time intervals governed by the person or extraneous agency which actuates the substation. However, when circumstances are such as seem likely to be most frequently found, the sub-station mechanism will include means for measuring the time between the first revision of loop conditioning and later revision or revisions,

so that such time will be adequate to prevent ,mutilation of code signals which are in course I of transmission. Under some conditions a time merely longer than any between closures within code signals but less than that between repetitions or rounds may be deemed preferable, but under many other conditions it will be deemed expedient that such time shall be greater than the longest open circuit interval incident to the formulation of any code signal in the main circuit.

Need for delay between actuating steps of substations, and need for action of the trip mech anism to disconnect the sub-station loop when acting in response to the first actuating step of a sub-station, as just referred to, arises from the fact that unintended signaling impulses would otherwise occur in the main line circuit;

which impulses would be likely to cause serious errors in the interpretation of signals.

If, however, each sub-station acts to apply. its ground connection only after a. time longer than any open circuit interval in any main line signal, throughout which time it has conditioned its loop to render the trip mechanism of its associated master station responsive to main circuit energization, and such trip mechanism, when it so acts, isolates such loop from the main line,

such isolation will always occur before ground connection application, when any sub-station is activated during the formulation of any signal in the main circuit of its associated master station.

If the master station formulates its code signal but once, it may be sufiicient to delay application of the ground connection for a time longer than any between impulses within code signals; but if such code signal is repeated one or more times, it becomes important that such delay time shall be longer than that between the last impulse of any one round and the first impulse of the next succeeding round.

Where operating circumstances are such that "it is desired that a presignal stroke shall be cially suited to operating conditions such that tripping magnet resistance is normally excluded from the main line current path and to ccnd7- tions such that it is desirable to minimize opportunity for unintended energization for the tripping magnet resultant from abnormal main line current surges, provides a tripping magnet winding so applied and connected that normal main line current flow through one of said winding will neutralize that through another part. 1 1

Portions of said winding are applied in substantially turn-by-turn, side-by-side relation-. ship, in order that opportunity for efiective excitation may be avoided, even during extraordinarily great current flow in portions of said winding which should neutralize each other, ex cept when conditions are such that current flow in a portion of said winding is extraneously caused to he in opposite direction or substantially difierent in intensity from that in another portion thereof.

Shunt loops are associated with said winding parts, respectively, and sub-station contacts are so connected in said loops that the first step of the actuation of the contacts of any sub-station will interrupt one of said loops, and, following the lapse of a predetermined time such as aforementioned, the other loop will be interrupted and one of the ends of at least one of said loops will be connected to the ground or other common return conductor; the loop end or ends thus grounded being such as communicate with portions of the tripping magnet winding which are reached by main line current flow only after traversing one, or the other, or both of the aforesaid p'arts of said windings.

For use under operating conditions such that it is deemed highly important to avoid unintended trip magnet energization resultant from sub-sta tion loop breakage, and such that constant inclusion of the resistances of trip magnet winding portions and of the sub-station loops in the main line current path is not deemed objectionable, an embodiment of this invention may be employed which provides a differentially wound trip magnet, such as that just referred to, the winding portions of which are correspondingly associated with the main line current path, except that one of the sub-station loops is serially connected between one side of the main circuit and one of the trip magnet winding portions and a second sub-station loop is connected between such of the winding portion ends as are reached from the main circuit only after traversing one or the other of said portions.

7 The sub-station contacts associated with these loops are so arranged that, in acting, they will initially interconnect the loops (thus substantially short-circuiting one winding) and thereafter will connect the ground or other common return conductor to the loop which interconnects the two winding portions, and will terminate the initial connection between the two loops.

For operating conditions such that it is deemed more important to decrease the number of the sub-station loop conductors from that required for the embodiments of this invention just described than to minimize opportunities for unintended energization of the trip magnet resultant from main line current surges, an embodiment of this invention may be utilized in which a trip magnet having a single Winding is normally shunted by a sub-station loop, and sub-station ing connections alternatively with one and the other of the sub-station loop ends, establishes such connection intermediate the ends of an asymmetric conductor so associated with the loop as to oppose the main line current flow in a direction such as would shunt the trip magnet winding.

For utilization in connection with signaling systems which do not provide a constantly available emergency signaling path between a main signaling circuit and the ground or some other common return conductor, and/or which do not maintain constant current flow in the main circuit path available for energization of a tripping magnet, an embodiment of this invention may be utilized in which sub-stations have normally short circuited magneto generators or other means for causing current flow in the sub-station loop such as will effectively energize the main station tripping magnet.

In the ensuing description and, more particularly, throughout the appended claims, wherever reference is made to interruption or to functionally interrupting of current paths which associate sub-station mechanism with a signaling or tripping mechanism electromagnet, it should be understood that the meaning denoted by such terms is intended to be inclusive of an increase in resistance of functionally significant extent; and wherever reference is made to increasing the resistance of any such path, the meaning denoted by this term is intended, insofar as the context permits, to be inclusive of interruption of such path.

Other characteristics of this invention, as well as certain more detailed features thereof, are shown by the accompanying drawings and set forth in the following detailed descriptions. It should be understood, however, that the embodiments illustrated, though practical, are by no means the only embodiments which this invention may assume, wherefore this invention is not confined to any strict conformity with the showing of the drawings, but may be changed and modified in various ways so long as such changes and modifications make no material departure from the salient features of this invention, as set forth in the appended claims.

In the accompanying drawings:

Figure 1 illustrates schematically and diagrammatically an embodiment of this invention believed to be suited for many practical situations;

Fig. 1A is a simplified across the line circuit diagram of the system of Fig. 1;

Fig. 2 shows a modified form of the mechanism of sub-station S of Fig. 1;

Fig. 3 shows a modified form of the contact controlling mechanism of Fig. 2;

Figs. 4 and 5 show modifications of certain portions of the mechanism of sub-station S of Fig. 1;

Figs. 6, 7, 8 and 9 show modifications of the system of Fig. 1 for meeting various operating conditions;

Fig. 10 shows a modification of Fig. 8 in which the auxiliary loop may, at times, be connected to the main circuit for supervision;

Fig. 11 shows another modification of Fig. 8 in which the auxiliary loop is separate and independent of the main circuit; and

Fig. 12 shows a modification to be referred to, of the master station of Fig. 1.

Circuit arrangement of Fig. 1

The embodiment of this invention schematically indicated in Fig, 1 comprises signal responsive and current supply equipment generally indicated at R, a master box signal initiating station at M, other initiating stations B, B", and auxiliary or sub-stations S S with associated answer backs A A For convenience, the equipment R will be at times referred to as the "central oifice. This equipment includes a normally effective battery NB, a ground or common return path battery GB,

a line signal manifesting instrument LI, manifesting instruments EI and GI respectively associated with rectifying units IR." and IR, all arranged substantially in accordance with the teachings of my Patent No. 2,034,017, dated March 17, 1936.

It will be readily understood by those skilled in this art that other arrangements of current supply mechanism and responsive instruments may be substituted for that indicated at R, such, for example, as disclosed by my Patent No. 2,018,656, dated Oct. 29, 1935. If, however, the arrangement of current supply mechanism is such that an alternating electromotive force is developed under any circumstances for signaling purposes between the line circuit and the ground, certain modifications should be made in other portions of the disclosed system, as will be hereinafter more fully pointed out.

The conductors 2|, 23, 25 and 21 serially connect the station B, master station M and station B between instrument LI and the parallel current paths including the instruments EI and GI.

The master station M comprises code signal formulating mechanism 3|, which may, preferably, be constructed substantially in accordance with my Patent 1,999,859, dated April 30, 1935; although many of the objects of this invention may be attained through the use of interfering formulating mechanism which applies a ground connection during each signaling closure, such, for example, as indicated in my Patent 1,528,596, dated March 3, 1925.

The relays Al and 43 are serially included in the main signaling circuit at respective sides of the formulating mechanism 3|. (See also Fig, 1A.) In order to meet many of the conditions found in practical service, it is desirable that a normally closed shunt current path should be provided around these relays, such shunt path to be interrupted during activity of the mechanism 3|. The contacts 45 are shown as controlling a shunt around these relays as well as around the formulating mechanism 3|. These contacts may be controlled in a manner analogous to that disclosed in my aforesaid Patent No. 1,999,859 for the control of the so-called train shunt contacts 6|, 63 and 8| of said patent.

The trip magnet 5| is provided for causing operation of the signal formulating mechanism 3| responsive to actuation of auxiliary or sub-stations associated therewith. In-as-much as the details of this trip mechanism, aside from the electromagnet structure, form no part of a broad aspect of this invention, such mechanism is merely here indicated in a simple schematic manner. Those skilled in this art are doubtless familiar with tripping mechanisms suitable for use in systems such as that indicated in Fig. 1, an example of such prior mechanisms being disclosed in patent to N. H. Suren, No. 1,575,947, dated March 9, 1926.

The trip magnet 5| has neutralizing differential windings so associated with the main circuit that normal current flow from said circuit will pass serially therethrough in such relative directions as will not cause effective energization'of this magnet; and so that if one of said windings is substantially short-circuited and there is normal main line current flow through the other winding, said magnet will be effectively energized. If the nature of the mechanism for'supplying current to this magnet is such that it may, under any circumstances, be subjected to alterhating current excitation, it should be of such type as to be effectively energized thereby.

Although the drawings indicate, as a matter of convenient illustration, that the windings of magnet may be applied in two distinct coils to separate portions of the core, I have found that best results are obtained if these windings are simultaneously applied in parallel convolutions, turn by turn; or at least, first a full layer of one and then of the other.

If actually applied to difierent portions of the core, abnormally large current flow in both windings is liable to result in development of an intermediate or anomalous pole between the windings, and of a strong free pole adjacent to the armature, and thus result in unintended tripping of the master station.

An end of one winding of the magnet 55 is connected to the main line conductor 23 and, through the normally closed contacts 65, to an end of the normally closed shunt loop 55. An end of the other winding is connected with main line conductor 25 through relays 43, 4B, and mechanism 3| (as well as, alternatively, through shunt contacts 45, when closed). Said second named winding end is also connected, through normally closed contacts 61, with an end of the normally closed shunt loop 51. The remaining ends of these windings are connected together and are further connected through contacts 64 with terminal 53. The remaining ends of shunt loops 55 and 51 are also connected to terminal 53 through various contacts presently to be described.

From the foregoing it will be observed that these shunt loops normally exclude substantially all of the resistance of the windings of the magnet 5l from the main circuit current path and, furthermore, the arrangement is such that should there develop in the main circuit a surge of current of such magnitude that the portion passing through the windings of the magnet 5i (due to shunt loop resistance) would be sufiicient to cause unintended tripping of the master station, where the magnet of the single winding type heretofore employed in master static-n trip mechanisms, the magnet 5| would not be thereby effectively energized, because current flow in one of its windings would still serve to neutralize that in the other of said windings.

Furthermore, because of the arrangement just described, the magnet 5| may be effectively energized by grounding the terminal 53 during shunt loop open circuiting, either in the event that the main circuit is broken 'at one side or the other of said magnet or in the event that said magnet is short-circuited, as for example, by .an accidental connection between conductors 23 and 25.

An armature 52 normally restrains actuation of tripping mechanism generally indicated at 33, 35, and is responsive to effective energization of said magnet 5! for causing the formulating mechanism 3| be set into action and for moving contacts 41, 49, 64, B5, 66 and 61 from their normal positions, as will be hereinafter more fully explained.

Auxiliary or sub-stations S and S are equipped with contacts which normally maintain the continuity of both of the shunt loops, and each stationhas mechanism (which will be presently described in greater detail) which mechanisms in operating, first act to interrupt one of theshunt loops and, after a suitable delay, act to interrupt the other of said loops and ground the portions of said loops which are associated with the terminal 53.

Although it is immaterial which of the shunt loops is initially interrupted by the sub-stations of any group, all sub-stations of a given system should be so connected that each will initially break the same one of these loops. (jtherwise, if two sub-stations were simultaneously operated and one broke one loop and the other the remaining loop, both windings of the trip magnet 55 would be simultaneously subjected to current flow, so that there would be no effective energization. correspondingly, it will be evident that all stations should be so connected that they will apply their ground connections to the portions of both of the loops leading toward terminal 53.

At each of these sub-stations, contacts I I and H are connected with conductors of loops 55 and 51 which lead toward the free or extreme ends of the windings of magnet 5!; while contacts 13 and 15 are connected with conductors of these loops which lead toward terminal 53; and contact I9 is connected with the ground.

An inverted L-shaped extension 33 is carried by the contact 13 for at times engaging the contact F5, as will be hereinafter more fully explained. I

Under normal conditions, contact I3 rests against contact H, and contact 15 rests against contact 11; contact 19 being spaced away from contact 13.

During operation of either of the sub-station contact actuating mechanisms, its associated contact 13 is moved away from contact H but is not, at first, moved far enough to engage its contact 79 or to carry its extension 83 into engagement with its contact 75.

Thereafter, further movement is imparted to its contact 13, carrying it into engagement with its contact 19, and carrying its extension 83 into engagement with its contact 15 so as to move the latter away from its contact 11, following action of such actuating mechanism in measuring the elapse of a predetermined time, which time, should, for many operating conditions, be greater than any open circuit interval incident to the formulation of any signal in the main circuit.

The novel form of answer back signaling equipment (comprising, for example in Fig. l, the loop 9|, battery 93, relays M and 43, signals A and A and contacts 85) is indicated in the drawings and herein rather briefly described in connection with the invention defined by the appended claims, for the purpose of emphasizing certain of the novel results obtainable through the use of this invention; but such answer back equipment is more fully described and is claimed in an application divisional herefrom, filed January 31, 1941, Serial No. 376,720.

The answer back loop 9| serially includes the auxiliary sub-stations S S and a current source herein indicated as the battery 93.

The ends of the loop 9| are connected to the normally open contacts of the relays 4| and 53 in such manner that the energization of either of these relays will complete the current path through said loop.

One or more general warning signals may be connected for response to the loop 9| as, for example, the warning bell 95.

In order that answer back signals will be manifested only at'actuated sub-stations, each sub-station is shown as having 'a pair of normally closed contacts 85, through which the current path of the loop 9| is normally maintained. Should it be desired that answer back equipment should act at stations other than those from which calls have been sent, contacts 85 should be maintained in open position at, or should be omitted from such stations.

Answer back signal responsive devices of desired type (typified by the tap bells 91 of answer backs A A shown associated with the sub-stations S and S respectively) may be associated with the various sub-stations in such manner as to be responsive to the answer back loop 9 I, during actuated conditioning of the respectively associated contacts 85.

Supplemental to the tap bell 91 of answer back A there is shown a lamp 99 and buzzer I! for operation from the current source I03 during actuated positioning of the hammer of the bell 91.

Actuating mechanism of s ub-station S The novel form of sub-station contact actus ating mechanism or circuit controller for signaling means indicated at sub-station S of Fig. 1, and in Figs. 2 and 3, will be herein briefly described in order to facilitate a complete understanding of the invention defined by the appended claims, but this circuit controller is more fully described and is claimed in an application, divisional herefrom, filed January 16, 1941, Serial No. 374,656, now Patent No. 2,301,924, dated November 17, 1942.

The mechanism of sub-station S comprises the collapsible bellows III, a lever II3 movable for compressing said bellows responsive to the spring H5 and for rocking the contact actuating lever I25, a trigger II1 for engaging said lever II3 to prevent such movement and subject to disengagement therefrom by manual or other actuation, an expansible chamber H9 connecting with the interior of said bellows through a restricted passage I2I and having a wall I23 movable responsive to the expansion of said chamber for swinging the finger I21 upon attainment of predetermined pressure within said chamber. The contact 13 is subject to partial actuation by said lever I25 and to supplemental actuation together with contacts 15 and 85, responsive to said finger I21.

Means should be provided, such as the spring I29, for assuring extended conditioning of the bellows III while the lever II3 is retained by the trigger H1.

The bellows III and the chamber II9 may contain air or other fluid, and the various parts should be so relatively proportioned that, when the trigger II1 has been disengaged from the lever II3, the spring II5 will act through said lever to compress the fluid in said bellows III and thereby to slowly force a portion of such fiuid through the passage I2I, whereby to build up pressure in the chamber II9 sufficient to cause the wall I23 to act through the finger I21 to impart suitable actuation to the contacts associated therewith.

The restriction of the passage I2I should be such that, from the commencement of the compression of the bellows III to the attainment of a pressure in the chamber II9 such as will cause full actuation of the associated contacts as hereinafter more fully explained, there will elapse a predetermined time. For many service conditions, this time should be longer than the longest open circuit interval incident to any signal in the main circuit.

The lever I25 is so associated with the lever II3 and the contact 13 that, when said lever II3 is moved by the spring I I5 to the position which it assumes when released from the trigger II1, the contact 13 will be moved away from the contact II, and thereby interrupt current flow in the shunt loop 55, for reasons heretofore more fully indicated.

The finger I21 is so associated with the wall I23 and with the contact 13 that when said wall moves from its normal position (after the contact 13 has been actuated by the lever I25, as already explained), the contact 13 willbe brought into engagement with the contact 19 -(thus grounding one end of loop 55, as already described) and so that the same or furthermovement of said contact 13, acting through the extension 83, will move contact 15 away from contact 11, thereby breaking the loop 51 and connecting one end thereof to the earth. Such movement of the finger I21 will also separate contacts 85, if used.

In order that contact 13 will be firmly actuated, and transient or chattering connections may be avoided, it is desirable that the steps of actuation of said contact shall be effected quickly by the finger I21. To this end, the free end of said finger is shown as having notches formed therein, and the spring pressed dog I3I so engages said notches that said finger will not move from its normal to its intermediate position until there is suificient pressure in the chamber II! to assure practically instantaneous or snap action, and correspondingly as to movement from intermediate to fully abnormal position.

Restoration of the mechanism of sub-station S may be effected, after it has acted following disengagement of the trigger II1 from the lever II3, by moving the lever II3 against the urge of the spring H5, and efiecting reengagement thereof by the trigger II1; whereupon the spring I29 will expand the bellows III, thus creating a relative vacuum in bellows III such as will cause the fluid which has been forced into the chamber H9 to return into said bellows, whereupon the Wall I 23 will be restored to its normal position, and (the lever I25 having been moved away from the contact 13 when the lever I I3 was restored) the various contacts associated with the finger I21 will return to normal positioning.

If operating conditions are such that it is found desirable to distinctively provide for a third operating step resultant from compression of bellows such as III, this may be accomplished as indicated in Fig. 2 by use of a supplemental chamber 2I9, the interior of which is connected with that of the chamber 2I9 through the passage 233, and through passage 22I with collapsible bellows 2| I, which correspond with the bellows III of Fig. 1.

The use of such a supplemental chamber will cause a distinctive added step of actuation to be imparted to the contact 13, whereby said contact will be first moved away from the contact 1I, either by the lever II3 actingthrough the lever I25 or resultant from initial movement of the wall 223 acting through the finger 2 21, and, thereafter, following a suitable delay, said contact 13 will be moved into engagement with contact 19 when the wall 223 of the chamber 2I9 is moved to its fully actuated position. Still later, following a second suitable delay, the finger 235 will be moved by the altered positioning of the wall 223' of :the chamber 2H) to cause the contact 13 to carry the extension as into enfanism which gage'ment with the contact T and thereby move .said contact 15 away from the contact 1?.

Likewise, as indicated in Fig. 3, the finger 335 (corresponding to the finger 235 of Fig. 2) may be utilized for neutralizing the effect of the actuation of the contact 13 by the finger 321. Said finger 321 is similar in action to finger 221 of Fig. 2, and is pivotally attached, at 328, to the free end of finger carrier 321; which carrier is pivotally supported at 325. With the arrangement shown, after the contacts. 13 and I5 have been connected to the contact I9 for a desired time (responsive to movement of the wall 323 away from its normal position) subsequent movement of the wall 323' will result in said contact 13 being permitted to move away from the contact I9 and such movement will carry the extension 83 away from the contact I5, permitting said contact 15 to reengage the contact H, where- .upon shunt loop 51 will be closed, shunt loop 55 will remain open, and the ground connection through contact 19 will be isolated from both loops.

Those skilled inthis art will recognize advantage of ultimately disconnecting the ground connection at an operated sub-station when such station is utilized in connection with a wellknown form of master station tripping mechanism, which mechanism is so arranged that it may be partially reset for the purpose of determining if the sub-station loop current paths have been restored to normal condition (as at all actuated sub-stations), and preventing a completion of restoration of the main station in the absence of normal loop conditioning.

t is evident that, in the absence of partial restoration of sub-station contact relationshipsuch as just described, both shunt loops would "remain open, and the trip'magnet would not be energized upon such partial restoration of the trip mechanism, because resultant current flow in one of its windings would neutralize that in the other winding.

It is further evident that, unless the sub-station ground connection is first disconnected, such partial restoration of the tripping mechanism of the main station will result in temporarily grounding the main circuit and thereby causing a central ofiice signal manifestation which might be objectionable under certain operating conditions, particularly if the trip mechanism must be permitted to return to fully tripped condition responsive to the rendering effective of such a ground connection incident to partial restoration thereof.

Actuatz'ng mechanism of sub-station S As an example of means, along lines of prior art mechanisms, which may be utilized for effecting actuation of contacts of sub-stations in accordance with the broader aspects of this invention, reference is madeto the sub-station mechis more or less schematically indicated in Fig. 1 at S disclosing clock-work mechanism whereby a predetermined series of changes in circuit conditioning may be effected in a sequence which is timed suitably for the purposes of this invention.

The mechanism at S? is arranged for response to manual actuation of the handle I51, which is carried by the shaft I59, together with the notched disk ItI and the escape wheel It3, each for movement independently of the others.

A spring I65 has its respective ends connected ing responsive to counterclockwise rotation of said handle around its pivot I59, so as to urge like rotation of said disk.

A segment I91 moves with said handle, and a face I59 of said segment is disposed in the path of the pin I'II, which is carried by the disk ISI, for limiting the extent of the rotation of said disk responsive to the spring I65.

The escape wheel I63 is driven by the disk I SI, acting through the spring pressed click I13, and the escapement I governs the speed of rotation of said wheel, and therefore of the counter clockwise rotation of said disk. a

The stops I1! and I19 are situated in the path of the handle I57, for limiting its angular movement to slightly more than that between adjacent notches in the disk I 6| The latch I8I is pivoted at I 83, and the free end of said latch so co-operates with the segment I51 as to be supported thereby other than when said segment is in the position which it assumes when the handle I5! is in or near contact with the lower stop I79, and, at such times, said latch may be moved by the spring I85 into the path of said segment and thereby retain such positioning of said segment. A handle I8! is associated with said latch to facilitate manual withdrawal thereof from the path of said segment.

A flexible brake I89 co-operates with the escapement I15 and is governed by the latch I8I, so that when said latch is supported by the segment I5! said brake will prevent operation of said escapement, and so that movement of said latch into the path of said segment will free said escapement from said brake.

A finger I9I, pivoted at I93, projects into the path of the stud I95 carried by the disk ItI; said finger being so formed and positioned with relation to said stud that, as said disk approaches 2 the limit of its counter clockwise rotation, said to said handle-andtosaid disk I6-I, for'tensionstud will engage said finger and move it from its normal to an extreme abnormal position.

The flexible contacts Ii, I9, 15, ll, i9 and are so associated with each other, with said latch 58! andwith said finger l fi'l, that contacts H, 13, and contacts i5, i7, and contacts 85 are normaliy engaged; that contacts ll, 13, wiil be separated whenever said latch I8I is positioned in the path of the segment I61; and that movement of the finger i9! from its normal toward its extreme actuated position will bring contact 53 into engagement with contact 79, and will cause a connection to be established between contacts 83, i5, and final movement of contact 13 by finger I9I will effect separation of contact 15 from contact 'l'a'; contacts 85 being meanwhile separated.

As heretofore more fully explained, contacts II, '53, are intended for serial inclusion in a master-station shunt-loop, contacts 15, 1?, for like connection in another such loop, and contact i9 for connection to the ground.

The timing of the rotation of the disk I9I, which is effected by the escapement I89, H5, is such that, from the freeing of said escapement when the latch ISI moves into the path of the segment 69? until the stud I95 so moves the finger I as to cause a connection to be established between contacts 13 and I9, there will elapse a predetermined time, which, for many service conditions, should be greater than any open circuit interval incident to the formulation of any signal in the main circuit.

From the foregoing it will be noted that, when the mechanism of station S as just described,

has come to rest, the contacts 13 and will remain connected to the grounding contact 19 and separated from the contacts H and 11 which are normally engaged respectively thereby.

As heretofore pointed out, this will result in continued grounding of portions of both of the shunt loops, as well as keeping both of such loops open.

For operating conditions such that it is desirable that the ground connection shall be terminated, and one of the shunt loops closed, before attempt is made to reset the master station, such results may be obtained by substituting the finger 49I of Fig. 4, for the finger I9I of Fig. 1; the portion of the finger 49I which is disposed in the path of stud I95 being so formed and positioned that, after said stud has depressed this finger for desired actuation of the associated contacts, said stud will pass beyond such actuating face before the disc I6I comes to rest, and will therefore permit the finger 49I to move to a position which allows contact 13 to move away from contact 19, thereby incidentally permitting contact 15 to move into engagement with contact 11.

It is evident that with finger 49I formed as shown, and when thus restored after the stud I95 has passed beyond the actuating face thereof, a portion of said finger 49I will be disposed in the restoration path of the stud I95, and must be withdrawn from such path before the disk I6I can be moved to its normal position. A handle 491 is therefore shown on the finger I9I, so that said finger may be manually moved to withdraw its obstruction from the path of the stud I95 at the same time that the handle I81 is employed for moving the latch I8I out of the path of the segment I61.

Operation of the station at for causing the starting of an associated main station, is accomplished by moving the handle I51 from its normal elevated position (adjacent to stop I11) into engagement with stop I19.

Such movement of the handle I51 will stretch the spring I65 and thereby urge rotation of the disk I6I together with the escape wheel I63, but the escapement I15 will be locked against operation by the brake I89 until said handle has nearly reached the stop I19, when said segment will be withdrawn from the path of the latch I8I. Thereupon, the spring I85 will move said latch into the path of said segment, and thereby lock the handle I51 and parts moving therewith from return to their normal position. Such movement of said latch will also cause contact 13 to be moved away from contact I! and will withdraw the brake I89 from restraint of escapement I15.

The disk I6I will thereupon act through the click I13 to rotate the escape wheel I63, and the escapement I15 will so time such rotation that the stud I95 will not engage the finger I8i (or the finger 49I, as the case may be) until the end of a suitabl predetermined time, following the movement of contact 13 away from contact 1|.

After the stud I95 has engaged the actuating surface of the finger I91, further rotation of the disk I66 will result in movement of the finger I9! such as will accomplish the sequence of contact relationships hereinbefore more fully described; after which, the rotation of the disk I6I will b arrested when the pin I'II overtakes the face $9 of the segment I61, in the position to which it has been moved.

After actuation as just described, the station mechanism can be restored to normal conditionmg by moving the handle I51 into engagement with the stop I11, having first swung the latch I8I out of the path of the segment I61 and, in the instance of a station using finger 49I, having swung said finger out of the path of the stud I95.

Such restoration of the handle I51 and of the disk I6I will permit the click I13 to enter the next notch in said disk and-the brake I89being now in holding relationship with the escapement I15the various parts will remain in their normal conditioning until the handle I51 is again moved to the stop I19.

For service conditions in which it is desirable that a sub-station similar to that at S may be caused to act by a force insufficient to move the handle I51 to effect stretching of the spring I65, such mechanism may be converted into a prewound type by applying thereto the parts indicated in Fig. 5, comprising a latch 58I for cooperation with the segment I61, with an independently moving, associated lever 599 carrying the flexible brake I89 and having an associated arm 599 for actuating contact 13 and for engagement witha trigger 5 I 1.

It will be evident that, with these parts, the handle I51 may be moved to the stop I19, and thereby stretch the spring I65, and the latch 58I will engage the segment I61 and retain the parts in such pre-set positioning, whil the brake I89 will hold the escapement I15 from operation until the trigger 5 I 1 is moved to disengage the free end of the arm 599', which arm will thereupon be moved by the spring 585, so as to withdraw the brake from restraining the escapement I15 and so as to move the contact 13 away from the contact 1 I, whereupon the various operative steps will occur as already described.

In resetting a station having the parts indicated in Fig. 5, the handle 588 will be used for withdrawing the latch 58I from the path of the segment I61, and such movement of said handle will bring the pin 581 into engagement with the lever 599, causing it to carry the brake I89 into engagement with the escapement I15, while incidentally permitting the contact 13 to move into engagement with the contact 1 I Description of Fig. 6

Should it be desired to utilize an arrangement such that breaks in shunt loops will not cause tripping of the master box, th shunt loop relationship to the tripping magnet, as indicated in Fig. 6, may be utilizedin the place of that indicated in Fig. 1. 1 V

Pursuant to the arrangement of Fig, 6, the main line current path from the conductor 23 normally includes the contacts 664, 665, the loop conductor 64I, a portion of the contact 643, the conductor 645, the contacts 669, one winding of the magnet 5| (see also Fig. 1), the contacts 661, the conductor 651, a portion of the contact 649, the conductor 65I, the contacts 668, the other winding of magnet 5|, from the remaining end of which latter winding the main linecurrent may pass through other circuit portions in a manner correspondin to that indicated in Fig. 1. g, a

During activated positioning'oithe contacts 654669, (as by the arm 33 of Fig. 1), contact 666 provides a current path from contact 664 which by-passes the windings of magnet 5| as well as the loop conductors, after the establishment of which the loop ends are disconnected from the main currentpath at open contacts 665, 661,668 and I569.

The sub-station transfer contact 653 normally engages thecontact 66,3, and the grounding contact 655 is normally spaced away from the contact 653; the arrangement of these contacts being such that, during a first step of actuation of the contact 653 (as by the lever I25 of station S of Fig. 1, or the latch 8| of station S of Fig. 1) said contact 653 will be brought into engagement with contact 649, and, during ensuing actuation of the contact 653 (as by finger I21 of station S of Fig. l or finger |9| of station S of Fig. 1) said contact 653 will be moved away from contact 643 and against contact 655.

During simultaneous engagement of contacts 643, 653 and 649, as just described, one of the windings of magnet 5| is thereby short-circuited; whereupon, normal current flow through the other winding will cause efiective energization of said magnet with the resultant tripping of the signal formulating mechanism, providing that the main line current path is then effective.

After contact 653 has been moved against contact 655 and away from contact 643, current may flow through either of the windings of the magnet 5| and through contacts 649, 653, 655 to the ground or other common return conductor, in ac cordance with possible broken main line conditions at one side or the other of the magnet 5|, and current may flow cooperatively to ground through both of said windings if the portions of the main line circuit at respective sides of this magnet provide a short circuit around it, as neither of its windings will then be short circuited between contacts 643, 649.

It should be understood that such ensuing movement of the contact 653, whereby a ground connection is established, will be effected only at the end of a suitable time, such as previously referred to, following the aforesaid first step.

Results characterizing use of the loop arrangement of Fig. 6 may be summarized as follows:

Both windings of the tripping magnet 5| and both sub-station loops and their associated contacts are under constant supervisory test from the main circuit.

- A break in either loop or its disconnection from respectively associated contacts 643, 649, opens the main circuit, but does not cause unintended tripping of the main station or render the magnet 5| unresponsive to application of a ground connection incident to actuation of an associated substation.

Accidental grounding of the loop 6M, 643, 645, gives a central office indication but does not cause unintended starting of the main station.

Accidental grounding of the loop 64?, 669, 651, will give a central office indication, and will be likely to cause unintended starting of the main station, depending upon the resultant degree of unbalancing of normal current flow in the windings of magnet 5|.

It will be noted that, inasmuch as the excitation of magnet 5! which might resultfrom cur rent flow in one of its windings is neutralized by that of like current flow in the other of its Windings, current surges in the main line path will sub-station loops, would be objectionable.

Description of Fig. 7

Where operating conditions are such that it is deemed inessential either that energization of the trip magnet will be assured in the event that such magnet is short circuited, or that no such energization will result from current surges in the main line, a single shunt loop arrangement, such as indicated in Fig. 7, may be substituted for double loop arrangements such as are indicated in Figs. 1 and 6.

Sub-stations S and S as here shown, have asymmetric conductors 169 associated as hereinafter more fully explained, so as to cause energization of their trip magnets during broken main line condition by a single application of the ground connection, while the arrangement of station S is such that application of the ground connection is needed, first to one and then to the other of the severed loop ends.

When asymmetric conductors are used, as indicated at stations S and S, the central office current source should be of such character that the direction of current fiow will not be other than normal, in any portion of the main line circuit, resultant from application of a ground connection thereto. Otherwise, application of a ground connection intermediate the ends of an asymmetric conductor such as 169, will, under certain conditions, fail to result in efiective energization of the associated tripping magnet. For this reason, when asymmetric conductors are employed as indicated in Fig. 7, a form of current supply such, for example, as that disclosed in applicants aforementioned prior Patent No.

2,018,656, should be substituted in place of forms having characteristics such as those of the current supply indicated in Figs. 1 and 1A.

In the interests of simplicity, main station loop cut off contacts, answer back facilities and various other features, the general nature of which is sufiiciently illustrated by Figs. 1 and 6, are omitted from Fig. 7, in which contacts of the three auxiliary stations 3", S, S are shown serially included in loop 751.

In the instance of station S sub-.stationcontact operating mechanism (which may be such as that indicated in stations 3 or S of Fig. 1) will first open the contacts 759 (as by the lever I25 of Fig. 1) and will, a suitable time thereafter, close the contacts (as by the finger I2? of Fig. 1).

In the instance of station the switch I59 may be first opened (manually or otherwise) and, a suitable time thereafter, switch 765 may be closed. For certain classes of service Where trained persons may be relied upon for actuating substations, and particularly where answer back signals are available, manual actuation of stations such as S might be relied upon; the operator being instructed to first actuate sufiiciently to open switch 156 and, thereafter, if the answer back signal does not indicate Within a reasonable time that the main station is formulating its code in a then effective current path (as hereinbefore more fully explained) the operator can further actuate the mechanism to efiect closure of switch 165'.

In the instance of station S operationg mechanism similar to such as contemplated for station S may be employed for first opening the contacts 159 thereat, and, a suitable time thereafter, withdrawing support of the contact '86! (as by movement of the finger I21 of Fig. 1) permitting said contact T8! to move into engagement with contact 183 and thereby ground one end of the shunt loop which has already been broken between contacts 159. Ensuing movement, as of the finger I21, thereafter moving contact 183 into engagement with the one of the contacts 159 which is connected to the other end of the shunt loop, and further movement of said contact 183 carrying it away from contact "I, thereby grounding the other end of the shunt loop, while not disconnecting the ground from one end before it is connected to the other end, so as to avoid possible formulation of an extra signaling impulse in the main line circuit.

With the arrangement of Fig. 7, it is evident that, so long as the loop contacts I59 are closed at the associated sub-stations, the normal shunted condition of the tripping magnet will be maintained. Upon breaking this loop, as by opening at either of said contacts 159 or at switch 159', the shunt around the tripping magnet will be broken and, if normal energizing current is then available in the main circuit, said magnet will be energized and will cause tripping of the associated main station formulating mechanism.

If the main circuit is open on any such occasion, it is evident that the breaking of the shunt loop will not of itself cause energization of the tripping magnet. However, in the instances of stations S and s", it will be seen that the ground connection is applied intermediate the ends of the asymmetric conductor 169, (which conductor bridges the break occasioned by opening the contacts 159 of S" or of switch 159' of S) in such relationship to the direction of current flow in the main line that said conductor I69 will prevent significant main line current flow therethrough other than in such direction as will be effective after such current has traversed the winding of the trip magnet 151; hence, if the main circuit is open at either side of said magnet, current from the remaining side of the main circuit may only reach the ground connection of an actuated station S" or S" after having energized the tripping magnet 15 I.

Similarly, in the instance of station 8',

grounding of first one shunt loop end and then of the other, assures effective energization of the trip magnet if there is a suitable electromotive force between either terminal of said magnet and the ground.

Use of asymmetric conductor arrangements, such as indicated for stations S and S is advantageous when sub-station structure is not such as to provide for application of a ground connection, independently, first to one and then to the other end of a severed sub-station loop.

In the use of forms of this invention in which the tripping magnet has a single winding shunted by a sub-station loop, as in Fig. 7, application of the sub-station ground connection intermediate the ends of an asymmetric conductor, as indicated at 169, avoids occasion for providing mechanism for separately grounding first one and then the other shunt loop end, as is contemplated by the arrangement indicated at station 8".

The use of asymmetric conductors is correspondingly desirable in sub-stations (such, for example, as station S in which all shunt loop alterations are, or may possibly be, eifected simultaneously.

Description of Figs. 8, 9, 10, and 11 In the instances of signaling systems in which tral oflice between the main line circuit and the earth, other-than during broken circuit conditions, systems arranged in accordance with Figs. 1, 6 and 7 would fail to effect tripping of the master station in the event that it becomes short circuited.

To meet these and certain other special circumstances, arrangements such as those indicated in Figs. 8 and. 9 may be utilized.

Referring to Fig. 8, the trip magnet I may be associated with the main circuit in the usual manner, or, if circumstances are such that it is deemed unnecessary to maintain main line circuit constant test of the shunt loop from the central ofiice, or should it be deemed undesirable. that there-be any electrical connection between the main current path and conductors which'connect sub-stations, the winding of this trip magnet maybe normally isolated from the main circuit; as by use of the cut-off switch I992 of Fig. 10, or by complete omission of such an interconnection, as indicated in Fig. 11.

The terminals of said trip magnet 85l are connected to the contacts 853 and 855, respectively, and contact 851 normally engages contact 853, while contact 859 normally engages 855.

The ends of the shunt loop 861 are connected to the contacts 851 and 859, respectively, said contacts being separable by main station mechanism in a manner analogous to the operability of contacts 64, 55 and 61 of Fig. 1.

In each auxiliary or sub-station there is provided a normally shunted magneto generator 81 l, with means 813 responsive to actuation of the generator for opening its shunt in a well known manner.

Such generators should preferably be of comparatively high resistance type, in instances in which the trip magnet 85l is subject to energization from themain line circuit, to the end that adequate energizing current for said magnet will be diverted to flow through the winding thereof when the shunt around any sub-stationgenerator is interrupted.

It will be evident that the actuation of any sub-station generator will cause effective energization of its associated trip magnet 85!, even in the absence of current flow in the main circuit. However, a low-resistance accidental short circuit around the winding of the magnet 85l might prevent energization of said magnet responsive to sub-station generator operation. If it is desired to safeguard against such a condition, and to assure effective energization of the magnet 85| even if a short circuit exists between the conductors 23, 25 of the main circuit, a resistance or reactance 855 should be included in the main circuit at one side or the other of the winding of the magnet 85] so as to oppose alternating magneto current flow around the tn magnet.

If it is desired to provide answer back signals for the system of Fig. 8, this can be accomplished by associating the magneto bells 815 with respective sub-stations, which bells may :be in series with the respective generators and controlled by the associated generator shunt, as shown, so as to 1be short circuited when the generator is at res In order that such bells shall sound in a manner which will identify the code signal of the associated main station, a contact 86| is normally spaced away from contact 851 and a contact 863 is normally spaced away from the contact 859 in such respective relationships that, during actuated positioning, contact 851 will engage contact BSI and contact 859 will-engage contact 853.

Relays 84! and 843 are controlled from the main circuit in a manner corresponding to that of relays 4| and 43 of Fig. 1, and the normally open contacts of said relays are connected in parallel with each other and between the contacts 86!, 853 so that, when the tripping mechanism has acted to move the contacts85'l and 859 from their normal positions, the bell N5 of the active station will sound only during effective closures of the main line circuit at one side, the, other, or both sides of the associated signal formulating mechanism. Hence, if operation'of the magneto generator is then continued, response of the associated magneto bell will be such aswill identify 1 the code number of the associated main station only in the event that such station is transmitting its signal through a then effective main line current path.

It will be noted that, with the arrangement of Fig. 8, the answer back bell is silent if the loop 861 is broken, but that it otherwise sounds throughout actuation of the magneto generator, even in the event that the tripping mechanism of the main station fails to act. Where some of those who might use sub-stations may be untrained in reading code signals, there is danger that such users may assume that any sounding of the answerback bell is a sufficient assurance that a call has been efie'ctively formulated in the main line circuit.

Such an assumption may result in a user of a sub-station failing to employ other means for summoning the fire department at a time when, for any reason, the associated main station fails to formulate its signal in a then effective main line current path. If operating conditions are such that action of this kind is deemed objectionable, the arrangement of Fig. 9 may be substituted for that of Fig. 8.

Referring to Fig. 9, the contacts 953 and 855, the relays 9M and 943, and the generators 9H, 9', are similar in operation to the contacts 853 and 855, the relays 8M and 843, and. the generators 8H, 8', of Fig. 3. Each of said generators having a shunting contact 9'53 therefor, similar to the contacts 813 of Fig. 8. An answer baclr loop 969 extends from contact 96!, serially through the magneto bells 975, 975 associated with various sub-stations, to one side of the normally open contacts of the relays 9M and 943, the other side of said relay contacts being connected to the contact 963.

Each sub-station magneto generator has a shunt 9T! normally short circuiting its associated magneto bell, and each of these shunts moves with the associated shunt 913 so as to break such bell short circuit throughout actuation of the generator.

Operation of any sub-station magneto generator of Fig. 9 will first cause energization of trip magnet 95L with resultant actuation of contacts 951 and 959 so as to transfer the ends of loop 961 from the ends of the winding of magnet 85| to the answer back loop 959 in which the normally open contacts of the relays s t! and 943 are included, in parallel with. each other. Consequent- 1y, the magneto bell 915 associated with the actuated station will only sound responsive to energizations of one or both of the relays 9M, 9 53.

It will be apparent that interconnection be tween the main circuit conductors of Fig. 9 may be governed by a switch, such as the switch M32 of Fig. 10, or that such an interconnection may be eliminated in a manner such as indicated in Fig- 11.

Normal operation, Fig. 1

Assuming that the main circuit is closed and free from accidental grounds and crossespand that the mechanisms at the master box M and at the sub-stations S S are conditioned for intended operation, there will be suitable current flow in the main circuit (see also Fig. 1A) from the battery NB, through instrument LI, conductor 2|, station B and conductor 23 to closed contacts 65 and to a free end of one of the windings of magnet 5|. Thence the current will divide and the major portion will traverse said contacts 55, the shunt loop 55 serially including the contacts H and 13 of sub-stations S and S to terminal 53, thence through shunt loop 51 serially including contacts 75 and 71 of substations S and S to closed contacts 61.

From the contacts 67, current flowwill proceed through the shunt contacts 45 to conductor 25, thence through station B" and conductor 2'! and through rectifying unit IR. and instrument E1 to the other terminal'of battery NB. There will also be a current path to the remaining free end of the winding of the magnet 5|.

Some'current will also flow through the windings of magnet 5|, due to the resistances of loops 55 and 51, but such current flow in one of said windings will neutralize that in the other, so that there will result no significant energization of said magnet.

Contacts 45 being closed, as already explained, will serve to short circuit the relays 4| and '43 as well as the mechanism 3|, thus preventing efiect'ive energi'zation of said relays, whose armatures will therefore be in retracted position, whereby to prevent current flow in answer back loop 9|. The windings of said relays 4| and 43 being also short ci'rcuited by the normally closed contacts 49 and 4T, respectively.

Operation now, of contact actuating mechanism of one of the sub-stations S S may be effected as follows:

Assuming utilization of mechanism such as that at sub-station S depression of the trigger I! will release the lever I l3 which will be moved by thespring H5, and act through the lever I25 to move the contact 13 away from the contact 1| and thereby interrupt current flow in loop 55. The entire current flow of the main circuit will thereupon pass through one of the windings of the magnet 5| while the other of said windings remains substantially short circuited by the loop 51. Thereupon, the magnet 5| 'will be efiectively energized, causing its armature 52 to effect release of the arm 33 which will then move in response to the spring 35.

Such movement of said arm will causethe code signal formulating mechanism to be set in operation or pulled, with incidental opening of the shunt contacts 45.

Such movement of the arm 33 will also cause opening of the contacts '41, 49, 64, 65 and 61, and will, at the same time, efie'ct closure of the contacts 66.

Such opening of the contacts 64, '65 and 5! will isolate the shunt loops 55, 51 from the main circuit, and such closure of the contacts 66 will short circuit both of the windings of the magnet 5|. Such opening of the contacts 41 and 49, supplemental to the opening of the shunt contacts 45, will remove all shunting paths around the windings of the relays M and 43, thus causing effective energization of these relays with resultant closure of their normally open contacts and commencement of current flow in the answer back loop 9!, causing energization of the signal 95.

When the lever II3 of the actuated station was moved by its spring I I as already described, such movement compressed the bellows III, causing the fluid therein to slowly pass through the passage I2I and build up a pressure inthe chamber H9 at such rate that, after the elapse of a time longer than the longest open circuit interval incident to any signal in the main circuit, the finger I21 will be so moved as to carry the contact I3 into engagement with the contact I9, and said finger I21 will further move said contact I3 far enough to bring the extension 83 into engagement with and thereby move the contact I5 away from the contact 11.

Although the ground path associated with the contact I9 will thus be connected to portions of the shunt loops 55 and 51 through the contacts I3, 15, such connection will have no effect upon the magnet 5| or upon the mainline current flow, because the loops 55, 51 will have been previously isolated from said magnet and main line current path, as already explained.

Incident to the actuation of sub-station contact I3 by the finger I2! previously referred to, the contacts 85 will be opened, and thereupon the associated tap bell 91 of answer back A will be rendered responsive to the answer back loop 9|, so that the associated bell 91 will be energized and, had sub-station S been operated, the bell 91 of answer back A would have responded and the lamp 99 would be lighted and the buzzer I9I would sound.

Thereafter, as the code signal of the mechanism 3| is formulated in the main line circuit, such formulation will cause identifying response by the warning bell 95 and by the tap bell 91 of the answer back of the operated station and, in the instance of answer back A will also cause flashing of its associated lamp 99 and intermittent sounding of the buzzer IUI, so that the person who actuated the sub-station will be assured that the intended code signal of the master station M is being formulated in an effective current path of the main circuit. Suitable warning will also be given to others, by the bell 95, that the signal of station M is being formulated in the main circuit responsive to a sub-station.

After the completion of the formulation of the code signal of the mechanism 3I, the contacts 45 will be again closed, thus short circuiting the relays M, 43, and thereby rendering the answer back loop 9| and the signaling devices controlled thereby unresponsive to any ensuing main line signals from other stations.

Had the tripping of the main station M been accomplished by utilization of mechanism such as indicated at sub-station the operation would have been the same as just described except that, instead of depressing trigger II! of station S the handle I51 of station S would have been moved into proximity or engagement with stop I19, whereupon the mechanism of station S would have operated as hereinbefore more fully set forth in connection with description of said mechanism, with resultant actuation of its contacts in a manner corresponding to that resultant from actuation of station S Restoration after tripping When it is desired to again normally condition the system, actuated sub-station or stations should first be restored. This may be accomplished in the instance of the sub-station mechanism indicated at S by withdrawing the lever I I3 from the bellows I I I to the position in which it is latched by the trigger H1. The spring I29 will thereupon extend the bellows I I I, creating a partial vacuum therein, and the finger I21 will urge compression of the chamber H9, so that fluid will be drawn through the passage I2I into the bellows III, the finger I2'I will be moved away from and thereby permit re-establishment of normal relationships between contacts II, I3, I5, I9 and 85.

In the instance of a station such as indicated at S restoration may be effected in the manner hereinbefore more fully explained in connection with the description of the mechanism of said station.

The shunt loops having been thus restored to normal closed condition, the tripping mechanism associated with magnet 5I of main station M should be restored, by moving arm 33 away from, and thereby permitting re-establishment of normal positioning of, the contacts 41, 49, 64, 65, 56, 61; and effecting latching of said arm 33in its normal position. The shunt around the windings of the magnet 5I through contacts 66 will thus be opened, and other shunts will be re-established around the windings of this magnet through the loops 55, 51. Short circuits will also be established around the relays 4| and 43, supplemental to the shunt 45.

The various parts will now be restored to conditioning for causing the formulating mechanism 3| to act responsive to operation of any associated sub-station.

Broken line operation If one of the sub-stations S S is set in operation at a time when the main line circuit is standing open as, for example, were the conductor 25 broken, the magnet 5| will not be energized when the shunt loop 55 is opened by previously de scribed movement of any one of the contacts I3 away from its associated contact 'II. However, when such contact I3 thereafter engages its associated contact 19, current will flow from one terminal of source GB through source NB, through instrument LI, conductors 2|, 23, as well as through station B, through one winding of magnet 5I to terminal 53 (shunt loop 55 being open), thence through part of loop 55 through contacts I3, 19, and the earth, to the other terminal of battery GB; with resultant energization of the magnet 5I, starting of the transmitting mechanism 3|, opening of contacts 45, 64, 65, 61, 41, 49, and closing of contacts 66; whereupon the ground connection established at the operated sub-station will be isolated from the main circuit.

Thereafter, the formulating mechanism 3I will act in a well known manner to establish a ground connection thereat, and to formulate the intended code signal in the main line current path thereby established. The relay 43 will respond to closures of such current path, causing action of answer back instruments identifying the formulated code signal as previously de scribed.

Had the line conductor 23 been broken, instead of the conductor 25, the operation would have been the same as that just described, except that the energization of the magnet 5I would not have from "contact '11, current flow will result inboth through the other winding is intheopposite di- Will act to cause main stat'ionM-to formulate the isolated from-the main circuit as previously devhe termed a pre-sig-nal stroke.

been-effected responsive .to mere engagement of the sub-station contact :73 with its contact "1'9, because-the current path thus established would have excluded both windings of the magnet .51. Such a path would proceed from one terminal of battery GB, through instrument .GI, rectifying unit IR, conductor 21, station B, conductor '25 shunt 45, contacts '61, loop 51 .(includingclosed contacts TI, 15 of stations S S to terminal'5i3; thence through .one side of shuntiloop 55, contacts'13, 19 of the operated sub-station and the earth, to the other terminal of source GB.

When, however, movement, of c'ontact"l3, acting through its extension tlfi moves contact "5 away from contact "11 at the actuated.sub-sta tion, the loop 57 'will'beflbroken, thus diverting current flow from the (path jjus't traced, so that it .will pass through one winding of the magnet 5|, '(instead of merelythroug'hthe loop'5l) with resultant.energizationof said magnet, and consequent formulation of the code signal of the main station M ina path l'including'condu'ctors 25, 2'1, and relay '"M; such formulated signal beingalso manifested by answerlba'ck instruments such as 95,"9l',"l'9, I'M.

:Operatz'on of short circuited maz'ms71aiion .Assuming thatthestationM is short circuited,

as byan accidental connection between conduc- "tors '23, .25, it is ev'identthat effective energiza- "tion of'magnet 5! will not "result from --mere' breakingof shunt loop tdas'bymovement of contact 13 away'from -contact-H. When, however, ."contact "13 engages contact l9 and, :acting through extension .83; moves "contact "Ida-way windings of magnet 51,; that through one winding being in the direction "norm-ally resultant from current flow in themaincircuit while that .40 rection' from such normal fiow.

Consequently, the two windings of magnetel will-no longer neutralize eachother, but will cooperate in causing effective energization ofthe magnet "5t, whereupon the tripping mechanism intended *code signal between" line *an'dgrou nd, with resultant response of instrument "GI -a well known manner, the shunt loops being first scribed, and relays ll Midi-3*Wl11'aCt'lnaCc0ldance with the code signal-so formulated, to cause manifestation of such signal by answer back instruments.

commencement of the code signal formulated by themain station,.which response mightwell This is because application of a :groundconnection at .a sub-station then causes current. ilow. through. a responsive instrument vat. the centralrofiice, and

. subsequent cutting .off of theshunt loops by the contact/s64, 65, 61 interrupts, such. current flow. Such a pre-signal stroke may serve to give notice of the fact that theensuing code signalisthe result or actuation of asub-station under zcondltionscwhich have caused the main station to. transmit its code through an emergency :path.

1Such a .pre-signal stroke should, be ofespecial advantage m the instance ofaishuntedout orv'short:

circuited main station, the condition or which might not otherwise be immediately disclosed.

,It will be noted that the "interval which el'apses between sucha pre signa'l stroke and the foammenoement of the ensuing code signal will be substantially that required for the main station mechanism to commence efiective signal formulation after having been started in action during broken line ,or shunted out 'm ain circuit conditioning.

If service conditions aresuch -thatit is undesirable that such pre-signal strokes -sh all be formulated, "a change in -*the =manner of con- "trol or contact 64 \m aybe-so-effected-that when tripping magnet -5 l has been effectively energized responsive to establishment of -a ground connection at an associated sub-station, thereby involvingcurrent now through a portionof shunt loop-5-5 or 51 or through both-as wel'las "through terminal 53'and-contacts 64, a' r'esu-ltant L path Willbe rendered efiectiveias*by a suitable lock-up relay) wherebysuch grounding path-4 will not be interrupted until replacement *thereof has been "efiected by the mechanism =31; with provision such that, in the event that the main station mechanism is 'of' the --so-called' perfect non inter-ference'and succession type, itwill be-short circuitedincidental to establishing such :lock-up path; to the end that such form-ula-ting mechanism will act=to apply its ground: path, :even if there -might otherwise be current flow P'therethrough because of continuationwof 'the:efiiective- -nessof a -sub-'stationground connection. Any

' -such supplemental JgIOllnd path :to :be finally ;.cleare'd"-from thei'main'circuitrfollowingeffective- "ness of the "formulating station-.ground..path-. and a prior tothefirstaction ofthe formulating station to break its ground path incidentto signal formulation.

Referring to Fig. .12; modifications are here shownof the master station of Fig.1, along. lines .such asjust indicated.

vParts shown in Fig.,-12.,unchanged from. Fig.,1 have been ggiven the sfian le reference numbers; and descriptions, of s'uchparts, and of their opera- .tionis not here repeated. ,Modified and added parts are here given number's ,priefixedby theletvter T.

The relay ,FI'I icontrols,. normally. open, contacts .TZDand T3,iand the winding vof ma net is serially, included in the current. path between. the lower one, of the. contacts. Stand the. interconnected ends ,ofithe'. windings .of the, magnet .51

The normally open contacts T4 ofr-thelior/rnulating. mechanism '3! are so governed as to be we closed in the, event of i defective conditioning of the. main circuit during formulating activity. ,of that mechanism, as, Jfoii examplejm theqm'anner i'indicated jin applicanfifs aforcmenti n ld latent No.i1',99'9, 9, fortbe cont ol of the iemer ency ground connection switchiESjthe're shown.

iTheone of. the contacts fT4 which ,iscQIinected "with lithe Hearth rests a ain' 't .L h' .sl -pplemeutal contact T5,, so long as said contacts (I-'4 are separated. Closure ofisaid contacts T 1 causesisolation of the Contact T5. therefrom.

.The relay contacts 1T2 1-control,..acurrent path from the contact ;T5-lto,:the end of-thevwinding -..of the magnet of the. relayQTl farthest. fromuithe intercon-nectedends, of thevmagnetvj5 l. v The. relay, contacts T3.,control:-an1 interconnection between-conduotorsin and 25.

a From the vforegoing, .it will ,be. evident that of the contacts T4.

Because of the establishment of this path, current flow between the earth and the conductors 23 and/or 25 will continue unaffected by opening .of the contacts 64 resultant from energization of the magnet Closing of the contacts T3 will short circuit the non-interference magnet T6, with the consequence that the formulating mechanism 3| will cause closure of the contacts T4 incidental to en- .suing operation of the formulating mechanism,

for reasons more fully explained in applicants aforementioned Patent No. 1,999,859.

Closure of the contacts T4 will result in termination of their connection with the contact T5, with resultant deenergization of the magnet of relay TI and opening of its contacts T2 and T3.

When the formulating mechanism is of the socalled plain or interfering type, the magnet T6 will be omitted, the contacts T3 will not be needed, and the contacts T4 will be closed throughout substantially all formulating activity of the mechanism 3i.

In any event, when there has been current flow for energization of the magnet 5| resultant from a connection between the earth and conductors 55 and/or 51, the effect of such current fiow upon the conditioning of the main line circuit 23, 25, will continue until replaced by grounding of said conductors 23, 25 through the formulating mechanism incidental to closure of its contacts T4.

Busy line operation parts will differ from that already described in but two principal respects:

First.--If the main line circuit is being held open incident to signal formulation at a time when the contact 13 of the operated sub-station is moved away from its contact I l, the trip mag-- net 5! will not be energized until the next ensuing closure in the course of the formulation of such signal.

Due to the delay following such movement of the contact 13 away from the contact H, and prior to movement of said contact 13 into engagement with ground contact 19 (and incidental establishing of a connection with and movement of contact away from contact TI), the shunt loop 5'! will still be intact and the ground connection will not have been rendered effective when the next ensuing closure of the main circuit is effected incident to formulation of the signal of the already acting station therein.

Consequently, the tripping mechanism will act of the loops .55, 51 from the main circuit (resultant from'opening of contacts 64, 65,51) will therefore occur before closing of the circuit 75 ground connection to either of the shunt loops, thus avoiding needless interference with the signal already in course of formulation in the main circuit.

Sccond.'Unless the closure which causes effective energization of the magnet 5| happens to be that following the conclusion of the signal of a previously acting main line station, it will be understood that if the mechanism 3| includes a so-called non-interference feature, such feature will prevent any interruption by station M of the code signal already in course of formulation, and if said mechanism 3| includes a socalled succession feature such feature will cause the code signal of station M to be formulated promptly after the main line is in condition therefor. If mechanisms of stations M and B are of plain or interfering type (such, for example, as those shown and described in applicants Patent No. 1,528,596, dated March 3, 1925), station M will proceed with the formulation of its signal just as if no other station was in action, and this will not cause station B to discontinue its formulating activity. Throughout such concurrent formulating activities, each formulating closure at station M will result in current flow through path from terminal of battery GB through GI, IR, 21, B", 25, 4|, 3!, and through the earth to terminal of said battery. Each formulating break of station M will interrupt that path. Correspondingly, each formulating closure at station B will result in current flow through a path from terminal of battery NB, through LI, 2|, B, thence to and through the earth and battery GB, to terminal of battery NB. Each formulating break of station B will interrupt this path.

It is evident that, under the conditions just indicated, the signals of stations M and B will be fully and correctly manifested by the instruments GI and LI, respectively.

The response of answer back instruments under busy line conditions will correspond with that under normal conditions already herein explained, in that, following tripping of the main station, the associated answer back instruments will manifest all ensuing signaling impulses to which either or both relays 4!, 43, respond.

Thus, if the tripped master station is of the non-interference and succession type and signaling impulses from some other main line station are formulated before such master station takes control of the main line, the answer back instruments will manifest all such impulses, thus enabling the sub-station user to know that the code signal of the main station which should respond to his call is being delayed because priority has been accorded to some other signal.

Should the master station be of the interfering type, the answer back instruments willindicate whether the code signal of such station is being formulated over a then efiective main line path in one direction or the other from the main station. If other interfering type main stations are active at both sides of a tripped interfering type station throughout itsaction, absence of answer back will give warning that the intended signal has not been sent.

Simultaneous sub-station operation I v If two or more sub-stations are operated ator about the same time and while the main circuit is closed, the tripping magnet will be energized as soon as one of the shunt loops is interrupted,

with results as already more fully described,

Correspondin'gly, if the main-circuit is open,-'or is shunted around the main station, the result of the actuationof twoo'r morestations will be the same as if but one station were operated; except that,sub'-stations operated one-after another under such circumstances, will-cause "en'- ergization of the tripping magnet only "when a sub-station applies its ground connection to a loop at a time when such loop is "notbroken by any other sub-station "situated fthere'in between the terminal '53 and such "ground connection.

Results of shunt loop defects Accidental rupture ofeithe shunt monster 51, while the'system is o't'herwi-se in normalbondition, will result in 'trippirrgfdf the master box with consequent formulation of itsf'si'gnal and incidental cutting oil ofthe ishunt-loops.

Simultaneous breakage of both loops will not cause trippingoi the master station, butwilra'dd theresistance of'both'winding'sof magnet '51 to 'the main line'cir'c'uit, 'thus "tending'to cause a change in currentfiow'which 'maybe detected at the'cent'ralofi'ice.

If one'shunt'loop is broken at on'eside of an actuated sub-station and "the otherl'oop at the other side, tripping of the main station will 'nevertheless be accomplished, becausethe sub-station ground connection Will the'nbe applied to both loops 55 and 57, assuring that so long as either loop is intact between an actuatedfstation and terminal 53, energization of magnet 51 ma be eiiected. There will, however, be'no response to operation of a sub-station when bothloops5'5 and 5? are broken between such station and' terminal 53. v

Grounding of either or both-of the 'shunt loops may be readily detected from the central o'fiice, but will not cause tripping of the master station so long as both of the shuntloops are unbroken,

and will not prevent tripping of the-master station from sub-stationswhile conditions of other portions of the system remain normal.

Operation of Fig. '6

Operation of a system arranged in accordance with Fig. 6 issubstantially the same as that'of a system in-accordance with-Fig. -1,-exeept-as follows:

The first step of sub-stationcontactactuation establishes a connection between contacts 643 and 649 through contact 653. If, during this connection, themain line circuit is closed, either because it-is in normal condition and no other stations are active or incident-tea closure in the signal of some other station, the magnet 5l'wi11 be energized and will efiect trip-ping of the master station, whereupon centac't 666 will-be'moved into engagement with contact-664and carry same J60 -act to cause contact 653 to be moved away from contact 6G3 andinto engagement with contact 355, thus applying a ground'corinection between the two windings ormagnet'sh c that s'aid'ma'gnet will be energized by current new either from conductor 23 or conductor"25fi6r""co operatively rs fromboth or the'se'conductors m pa'rauel, should there be an "accidental connection between them. Operation ofTig.

Operation o'f 1 a system arranged in accordance with Fig. 7 differs from that herein before described -in connection with other embodiments of th'is invention, in respects as fcllowsz Under "normal 'conditio'ns, "substantially all of the 'i'iiain line current is diverted "around magfiet 15| threu'ghshunt looplfil.

actuation o'f statidn S first 'results in opening or-contacts 159, thus suspending normal-direction'o'f "current fiow in l'oo'p T5L becauseof the blocking action of rectifie'rsfl 69.

After'afpredetermind time'C-sueh as herein-berare 'de's'cribed) contacts 165 are closed, thus a'pplying a-ground connection inter-mediate t'o the ends of the rectifier or asymmetric conductor I69. Ii,-'now, there is-a suitable positive electromotive force between conductor 23 "a'n d-tlie earth, current' 'wi11 flow' through the'winding of magnet 15|-and the lowerlp'ortion of asymmetric conducter 'l'eeto the groundconne'ction, thus effectively energizing said magnet. If thereis alike negative pote'ntial between conductor 25 and the earth, 'current'will-fiow from the-earth'through contacts "(-65, the upper portion oi asymlnetric c'o'n'ductor 169 and the windingefmag'net'lel to conductor 2 5.

Corr'espondingly, in using station S, the

switch T59 is moved so -as to' interrupt the current path there-through, preferably, at firsh without b'r in'gi ng switch JSWi-h-"pdsitihn to close its g ioundfconnection. Then, after a suitable time,

switch 165' is moved to close its ground connection. Otherwise; its action will correspond with that of stations".

It will be evident that if, for example, in "a station such as S the ground connection is established at or about the time that the shunt loop path is broken and when the main line circuit is closed, there will be-a needless pre-signal stroke manifested at'the central ofiice, but the operation of the system will be otherwise unchanged.

In the instance of station S, the shunt loop is first interrupted between contactsl59,"aground connection is next applied between contacts 18! and 183, then between I83 and bothlal and'the upper contact of 159, after which 183 is moved away from 18!. 'Whi1e contacts "FBI and 183 are connected, the lower end of'the winding of magnet 15I is grounded, duringthe short timethat 183 connects both 1 8! and 159, both ends ofthe winding of magnet 15! are grounded, and when contact I83 connects the upper contact of 159 only, the upper terminal of the Winding of magnet 15l is grounded. In other words, after opportunity has been afforded forthe magnet'1 5l to be energized by normal current flow in the main line, a groundconnection is applied first to one terminal of-the winding and then-tothe other terminal of the'wi'nding; so that if there is a potential between either end of thiswinding and the earth, this magnet will beefiectively energized, and the connection to one end is not broken until that to the other endhas'become effective, so as to avoid a needless "extrapre-sig na1stroke in the central office.

igll, 6}, will cause itsnormally closed contact "873 to be ri ened, 'tnus imerposmg the-resistance of the generator and that of the bell 815 into the normally closed shunt loop around the winding of magnet 85L Thereupon, if there is current flow between conductors 23 and 25, said magnet will be effectively energized. In the absence of current flow between conductors 23 and 25, the current resultant from the actuation of the magneto generator will cause energization of the magnet 85l and will cause the associated bell 815 to sound. If there is an accidental short circuit between conductors 23 and 25, the reactance 865 will cause sufficient of the alternating current from the active generator to be diverted through the winding of magnet 85| to assure effective energization of this magnet.

When the master station has been tripped, as just indicated, its contacts 851, 859 will be moved away from its contacts 853, 855, and into engagement with its contacts 851, 853, respectively. This will isolate the loop 861 from the magnet 85l and from the main line conductors 23 and 25,

and will prevent further response of the associated bell 815 other than during signaling closures in the main line circuit which effect energization of either or both of the relays BM, 843. It will therefore be evident that continued operation of the magneto generator will cause its associated bell to sound the code signal formulated in the main circuit in a manner analogous to that already described in connection with Fig. 1, other than that, in the instance of the system of Fig. 8, no extra wires are required between the master station and the sub-stations for effecting the operation of the answer back bells, and the further fact that an associated bell 815 will sound throughout operation of its generator 81 I, so long as the shunt loop 861 remains closed even should tripping of the master station not be accomplished.

Operation of system of Fig. 9

The relationship between the magneto generators 911, 91! and the magnet 95! are similar to those of corresponding parts of Fig. 8, but the relationship of the answer back bells 915, 915 differs in that these bells are connected in a separate answer back loop 969, controlled by bellshunting switches 911, 911 at the respective generators.

Operation of a generator 91! will effect tripping of the master station through energization of the magnet 95l in a manner corresponding to that described in connection with Fig. 8.

Until the master station has been effectively tripped, the bells 915, 915 will remain silent.

After the master station has been tripped, resultant movement of contacts 951, 959, into engagement with contacts 96 I, 9-63, respectively, will connect the answer back loop 959 in series with the sub-station loop 951 through the local contacts of relays 941, 943.

Thereafter, continued operation of the associated generator 91! will cause its bell 915 to sound (shunting contacts 911 being held open by the operation of the generator) such sounding being co-extensive with closures of the contacts of either or both relays 94 l, 943.

Alternative embodiments While certain specific embodiments of thi invention have been illustratively indicated in the accompanying drawings and hereinbefore described in considerable detail, it should be understood that this invention is not limited to such embodiments or details, nor to any of them, ex-

cept insofar as they are defined by limitations fi within the terms of the annexed claims, in which it is intended to claim all generic and specific features inherent to this invention as broadl as is permissible in view of the prior art, inclusive of all statements of the scope of this invention which, as a matter of language, might be said to fall between the following.

I claim:

1. A signaling system having a normally energized main circuit, signaling mechanism including an electromagnet having winding portions connected serially with said circuit and opposingly with each other, two comparatively low resistance current paths normally shunting such winding portions, respectively, for preventing effective energization of said magnet, an independent conductor, means for maintaining an electromotive force between said circuit and said conductor, and sub-station mechanism associated with said paths, and operable for functionally interrupting one of said paths for causing effective energization of said magnet from normal main circuit current flow, for then likewise interrupting the other of said paths and for connecting said conductor with the end of one of said paths which leads to such end of the associated winding portion as is directly connected with an end of the other winding portion.

2. A signaling system having a normally energized main circuit, signaling mechanism including an electromagnet having winding portions connected serially with said circuit and opposingly with each other, two comparatively low resistance current paths normally shunting such winding portions, respectively, for preventing effective energization of said magnet, an independent conductor, means for maintaining an electromotive force between said circuit and said conductor, and sub-station mechanism associated with said paths, and operable for functionally interrupting one of said paths for a time measured by the operation of said sub-station mechanism for causing effective energization of said magnet from normal main circuit current flow, for then likewise interrupting the other of said paths and for connecting said conductor with the end of one of said paths which leads to such end of the associated winding portion as is directly connected with an end of the other winding portion.

3. A signaling system having a, normally energized main circuit, tripping means including an electromagnet having winding portions connected serially with said circuit and opposingly with each other, said means trippable responsive to energization of said magnet, two comparatively low resistance current paths normally shunting such winding portions, respectively, for prevent- 7 ing effective energization of said magnet, controlling mechanism responsive to tripping of said.

- first named means for isolating said paths from said circuit, an independent conductor, means'for maintaining an electromotive force between said circuit and said conductor, and sub-station mechanism associated with said paths, and operable for functionally interrupting one of said paths for a time measured by the operation of said substation mechanism for causing effective energization of said magnet from normal main circuit current flow, for then likewise interrupting the other of said paths and for connecting said conductor with the end of one of said paths which I leads to such end of the associated winding portion as is directly connected with an end of'the other winding portion. 

